Composite fuel and method of preparation



Patented July15, i947 COMPOSITE FUEL AND METHOD OF PREPARATION ichardS. Vose', Swarthmore, Pa... assignor to Sun Oil Company, Philadelphia, Pa., 9. corporation of New Jersey No Drawing.

7 This-invention relates to composite fuels and improvements intheir manufacture and particularly concerns fuel compositions comprising a dispersion of carbonaceous material,v such as coal, lignite, peat or charcoal, in liquid hydrocarbon material such'asgpetroleum oil'or coal tar oil. the preparation of fuel compositions .of the aforesaid type which are substantially stable and which, accordingly, have little or no tendency for suspended particles to'separate from the mixture during prolonged standing.

- Fuels of the type with which the present invention isv concerned have long been known and havegenerallyrbeen referred to'in-the art as colloidal fuels, although this term often is not a true indication of .thedegree of subdivision of the dispersed carbonaceousparticles. Ordinary "methods of manufacture usually produce fuels containingparticles ranging in size from true colloidal to "considerably greater dimensions.

Buch fuels .therefore have a tendencyfto be unstable due to settlement of thelarger sized particles w'h'en ,the mixture is permitted toflstand. In order' to overcome this disadvantage various means adapted to improve stability have been proposed, and these generallymay be classifled as twotypes. One type comprises further. reduction in particle size untilthe particles arein suchstate of subdivisionthat substantial settling will not occur. Disadvantages of methods ofthis type are that special and expensive equipment is required in order to effect the further subdivision and that power consumption is high. The other type comprises adding to the dispersion a stabilizing agent, such asso'ap, coal tar, starch, casein,.-gelatin or. rubber, which helps to maintain the carbonaceous particles in suspension. Such stabilizing agents have-a thickening effect on the mixture, often causing the formation of a thlxotropic gel, and so increase the: viscosity of the mixture that subsequent pumping and preheating is rendered diflicult. Methods employing a'combination of the two,above-men,.- tioned means of improving stability also have been proposed.

The present invention is directed to and provides a novel and distinctly advantageous method of preparing stable fuel compositions, wherein neither the aforementioned reduction of particle size to substantially colloidal dimensions nor the use of added stabilizing agents is required. In accordance with the invention the The invention has;for its principal object I pplication November 10, 1943, Serial No. 509,758

s c a ms. (CI. 4451) tained with usual commercial equipment, in a liquid hydrocarbon fuel, subjecting the dispersion to heat treatment, while maintaining the dispersed particles in suspension, for sufficient time to cause a relatively sudden change in physical properties of the mixture including a marked increase in viscosity, and then blending the thus treated mixture with additional liquid hydrocarbon fuel to reduce the viscosity to a suitable value and thereby-form a fuel composition having desired stability. I have discovered that a dispersion of finely divided carbonaceous particles in llquidhydrocarbons, such as coal in oil, when subjected to suitable'heat treatment, will, after sufllcient time of treatment, suddenly and unexpectedly thicken. 'The thus thickened mixturewill have no substantial tendency to .separate onprolongedstanding. Further, I have discovered that the thickened mixture then may be'blended' with further amounts'of liquid'hydrocarbons to produce a mixture having suitable fluidity and that the resulting composition also will be stable, even though the original dispersion contained particles of sufficient size'to settle out and in spite of the fact that the treatment. resulting in the sudden-thickening action brings about noappreciable reduction in particle size. 7 r The cause of the surprising change in physical properties of the suspension when treated in .ac-

cordance with-the invention is not understood and 'whether it is due to chemical or physical action orqto both is not known. Regardless of the explanation which eventually may be forthcoming, the phenomenon provides a simple and to suitable treating temperature, which need' not be excessively high, and, in .case the mixture is-fluid at that temperature, may be agitated in any manner effective to keep the .particles dispersed; for example, the mixture may be continuously pumped through a. circulatory system or may be continuously-stirred in a vessel by means of vany suitable stirring device. In case ahigh proportion of coal is, utilized and the mixture correspondingly is suiiiciently viscous, or plastic, so that the dispersed particles will not settle out to substantial extent, the mixture may merely be subjected to heat treatment without mechanical agitation. .The final step of blending th thickened mixture resulting from the treating step may be accomplished in any known or desired manner, for instance merely by adding the additional oil and stirring the mixture until it becomes uniform. Thus all steps of the process may advantageously be carried out in more or less conventional apparatus, and the process therefore may be practiced without the more expensive grinding or pulverizing devices and without special addition agents.

,In the novel treating step the time of treatment required to bring about the sudden change in physical properties of the suspension mixture varies with the treating temperature, the lower the temperature the longer being the time required. Accordingly, it is preferable touse a temperature above about 150 F. since lower temperatures necessitate treatment over such an extended and unreasonable period of time that the process becomes impractical. A temperature of about 175 F. is suitable for practical operation,

and any higher temperature up to either that at which substantialcracking of the mixture begins to occur or that at which the mixture begins to boil at the prevailing pressure, whichever temperature is the lower, may be utilized.

The treating time also depends to considerable extent on the particular oil used as the fluid constituent of the fuel composition. With one type of oil acertain period of treatment will be required to bring about the relatively sharp change in. physical properties, whereas with another oil and at the same treating temperature a considerably longer treating period may be necessary to effect the change or, on the other hand, a considerably shorter period may suffice. The requisite time of treatment also may depend on the particular type of carbonaceous material utilized in the composition.

The carbonaceous material dispersed in the oil should be in finely divided form but the degree of subdivision. is not critical. Excellent results'have been obtained with a degree of fineness such that 80-85 .per cent of the granular carbonaceous material will pass through a 200 mesh sieve; however, greater or less subdivision is suitable. Standard pulverizing or grinding apparatus maybe utilized to prepare the carbonaceous material in suitable form for dispersion in the oil.

The proportion of carbonaceous material which may be utilized in the dispersion mixture that is subjected to the novel heat treating operation may be varied over a wide range from a few per cent to and including major percentages. In case a relatively low percentage is used the heat treated mixture will be sufficiently fluid so that subsequent blending with additional .oil will not be necessary; however, the proportion of coal in the composition Will be less than that normally desired. Accordingly, it is preferable to use higher proportions, for example 30-50 per cent coal by weight in the mixture, so that after treat- 'ment and subsequent blending to desired viscosity thefinal composition will contain dispersed solids in amount customary for fuels of this type. The thermal treatment of mixtures containing such proportions usually produces a composition having viscous, gel-like properties rendering it un-' suitable for use per se as fuel. However, the

blending of this material with even a small proportion of additional oil destroys the gel-like properties and reduces the viscosity to considerblended with the treated mixture in order to attain desired fluidity. The use of such high proportions of coal is disadvantageous in that subsequentblending is more difllcult, necessitating the use of special apparatus which usually is not commercially available in sizes required for manufacturing commercial quantities of the fuel composition. In practicing the process it accordingly is preferable to treat an oil-coal disperslon having a. coalcontent within the approximate range of 30-50 per cent.

The following examples are set forth as specific embodiments of the invention-and are to be construed merely as illustrations and not as limitations thereof;

Example I An anthracite coal was pulverized to a fineness corresponding to the following sieve analysis:

Per cent Retained on mesh 0.1 Retained on mesh 0.1 Retained on 200 mesh 16.2 Passing through 200 mesh 83.6

Total 100.0

and 40 parts by weight of the powdered coal was mixed with 60 parts by weight of Bunker C fuel oil having a Furol viscosity of 48/122" F. and an A. P.:I. gravity of 16.5. The mixture was heated to about F. and held at this temperature for a prolonged period of time during which the dis- Furol viscosity before heat treatment 200/122F. Furol viscosity after heat treatment- 355/122" F.

The heat treated mixture, which had somewhat gel-iike'characteristics at room temperature, had no discernible tendency toward settlement of coal particles over a long period of standing. In order to produce finished fuel compositions the mixture was blended with various amounts of the Bunker C fuel oil to form blends having coal contents and viscosities as tabulated below:

' Furol Weight Per Cent Coal in Blend None of the blends exhibited any of the gel-like characteristics and none had any apparent tend- Viscosity at Furol Weight Per Cent Coal in Blend Viscosity at All of. these exhibited substantial separation of coal particles on standing for 36 hours at room temperature. Since the viscosity range of these blends overlaps that of the blends prepared in accordance with the invention, these results show that the difference in stability characteristics in the two cases is not due to any viscosity difference but to some unusual stabilizing effect brought about by the novel heat treatment.

' Example II In this example the same coal pulverized to the same fineness as in Example I was used, but the liquid hydrocarbon constituent was a residual oil obtained from a thermal cracking operation and having an A. P. I. gravity of 10.5 and a Furol viscosity of 15/122" F. A blend of 50 parts of the coal and 50 parts of the oil was prepared and was found to have a Furol viscosity of Til/122 F. The blend exhibited substantial settlement of particles when allowed to stand for 36 hours at 80 F. The mixture was subjected to prolonged heat treatment at 175 F. in similar manner as in Example I. After 63 hours of such treatment it suddenly thickened, resulting in a product having gel-like characteristics and such low fluidity that its viscosity could not be determined. Thismaterial was blended with various amounts of said residual oil to form blends having the following coal contents and viscosities:

None of these blends had the gel-like characteristics of the unblended heat treated mixture and all were stable'with regard to settling of suspended particles.

Having described my invention what I claim and desire to protect by Letters Patent is:

1. In a method of producing a composite fuel composition comprising a mixture of a liquid hydrocarbon fuel oil and finely divided, carbonaceous material, the step of subjecting such a mixture to a heat treatment comprising maintaining the mixture at a temperature above 150 F. and below the cracking temperature of the liquid hydrocarbon fuel for such a prolonged period of time as to bring about a relatively sudden, as distinguished from a gradual, marked increase in viscosity, said fuel beingjcharacterized by stability with respect to settlement of contained carbonaceous particles evenwhen diluted with a substantial proportion of added liquid hydrocarbon fuel of relatively low viscosity to substantially increase its fluidity.

2. The method defined in claim 1 followed by adding to the stabilized mixture sufllcient additional liquid hydrocarbon fuel oil to increase fluidity to the degree required to render it flowable without pumping or preheating.

3. Method of preparing a composite fuel which comprises dispersing finely divided carbonaceous particles in a liquid hydrocarbon fuel oil, heating the resulting mixture, while maintaining the dispersed carbonaceous particles in suspended state, to a temperature above F. but below a temperature effective to produce substantial evolution of vapors and below the temperature at which the oil starts to crack for such period of time as to effect a relatively sudden marked increase in viscosity, thereby to form a fuel composition characterized by stability with respect to settlement of contained carbonaceous particles.

4. The method defined in claim 1 wherein the said mixture contains at least 30 per cent by weight of carbonaceous particles.

5. The method defined in claim 1 wherein the finely divided carbonaceous material is anthracite coal and the liquid hydrocarbon fuel is a residual type fuel oil.

' RICHARD S. VOSE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

